Gluconeogenesis Flashcards
What is Gluconeogenesis?
It is the synthesis of new glucose from non carbohydrate sources
Where does Gluconeogenesis take place?
Takes place in the liver and a little in the kidneys
Give some precursors of Gluconeogenesis
- Lactate
- glycerol
- Amino acids
What does Gluconeogenesis require/
Consumes ATP
Is Gluconeogenesis the reverse of glycolysis?
NO
Which steps does Gluconeogenesis need to by pass and what?
Needs to pass the 3 stages:
1. conversion of glucose into pyruvate
2. Glucose into Glucose-6-phosphate
3. Fructose-6-phosphate into Fructose1-6- bisphosphate
These 3 reach release the most energy in glycolysis so gluconogenesis needs to bypass these steps
Go through the stages of Gluconeogenesis
- Pyruvate into oxaloacetate
- oxaloacetate into phosopoenol pyruvate
- phosopoenol pyruvate into 2- phosphoglycerate
- 2- phosphoglycerate into 3- phosphoglycerate
- 3- phosphoglycerate into 1,2 biphoshpglycerate
- 1,2 biphoshpglycerate into Glyceraldehyde 3 phosphate
- Glyceraldehyde 3 phosphate into fructose 1,6 biphophate
- fructose 1,6 biphophate into fructose 6 biphophate
9 fructose 6 biphophate into glucose 6 phosphate - glucose 6 biphophate into glucose
What does the first by pass step start with?
Starts with pyruvate
How does the first by pass step occur?
- Pyruvate dissolves into the mitochondria
- It is converted into Oxaloacetate via Pyruvate
carboxylase - Oxaloacetate is converted into malate via Malate
dehydrogenase - Malate then leaves the mitochondria
- Malate is converted in Oxaloacetate via Malate
dehydrogenase - Oxaloacetate is converted into Phosphoenolpyruvate via Phosphoenolpyruvate carboxykinase
What does Pyruvate
carboxylase do?
Converts pyruvate into Oxaloacetate this reaction releases ATP
What does Malate
dehydrogenase do?
Converts Oxaloacetate into malate this reaction releases NAD+
What does Malate
dehydrogenase do?
It concerts malate into Oxaloacetate this reaction releases NADH
What does Phosphoenolpyruvate carboxykinase do?
Converts Oxaloacetate into Phosphoenolpyruvate
After Phosphoenolpyruvate has formed what can happen to it?
- It can either form 2-Phosphoglycerate
2. Can be re converted into pyruvate
How is the conversion of Phosphoenolpyruvate into pyruvate stopped?
Excess glucagon prevents pyruvate kinase from working so pyruvate doesn’t form so glycogen isn’t broken down
State the second step of glycolysis we need to bypass in Gluconeogenesis
We need to reverse the Conversion of Fructose
6-phosphate into Fructose
1,6-bisphosphate
How is the conversion of Fructose
6-phosphate into Fructose
1,6-bisphosphate
reversed in Gluconeogenesis?
By the enzyme 1,6-bisphosphatase that converts Fructose
1, 6-biphosphate into Fructose
6 phosphate
How is the conversion of Fructose
6-phosphate into Fructose
1,6-bisphosphate and its reverse controlled?
It is reciprocally controlled Via Fructose 2,6 biphosphate AMP and Citrate ATP H+
Citrate increases the effectiveness of Fructose
1,6-bisphosphatase so more fructose 6 phosphate made
Fructose 2,6 biphosphate AMP increases the effectiveness of Phosphofructo-kinase so increasing the production of Fructose 1,6-bisphosphate
State the third step of glycolysis we need to bypass in Gluconeogenesis
We need to reverse he conversion of Glucose into glucose into glucose 6-phosphate
How is the conversion of Glucose into glucose into glucose 6-phosphate reversed in Gluconeogenesis
Via the enzyme Glucose
6-phosphatase which converts glucose 6-phosphate into glucose
What is Glucose 6-phosphatase dependent on>?
Magnesium
During prolonged fasting how does our body get energy?
It breaks down our fat stored to release fatty acids ad glycerol backbone
How are fatty acids used to obtain energy?
They undergo gluconeogenesis
What happens to glycerol That is formed via the breakdown of fat stores?
- Glycerol is converted into Glycerol Phosphate via glycerol kinase
- Glycerol Phosphate is then converted into DHAP via NAD+ and glycerol phosphate
dehydrogenase
What does glycerol kinase do?
Breaks dow glycerol into glycerol kinase
What does glycerol phosphate
dehydrogenase do?
Converts Glycerol Phosphate is then converted into DHAP
When is lactate used as a glucose precursor?
During vigorous exercise lactate is
produced in anaerobic muscle and
by glycolysis in erythrocytes
How can lactate be used as a glucose precursor
Lactate is converted into pyruvate via Lactate dehydrogenase
in the cytosol in the liver cells to produce NADH
What does Lactate dehydrogenase do?
Converts lactate into pyruvate
Give the overall conversion o pyruvate into glucose
2Pyruvate +4ATP +2GTP+ 2NADH+ 2H+ + 6H2O
->
Glucose + 2NAD+ + 4ADP +2GDP + 6Pi+ 6H+
How man high energy phosphates are needed to convert pyruvate into glucose?
6
State the over all free energy change of gluconeogenesis
-16kj/mol
State the over all free energy change of glycolysis
at least -63kj/mol
Can both glycolysis and gluconeogenesis occur at high rates simultaneously?
no as they are regulated allosterically and by covalent modification
